I post a lot of typing errors also
My solution to school shootings is limited entry to the school with metal detectors and armed security guards
Many people reject that idea but its the same method used to secure other public places
Schools have many, many, many doors to be up to fire code. You would have to have metal detectors at every door, which is inordinately expensive. Schools wouldn't do it--they can't--which makes "beating the metal detector" as easy as slipping in a side door by having it propped open, or a student hold it open for you. This would show up on a security camera later, but it's not like your identity would be a secret after you open fire.
You're not going to like this answer, and I don't care. Some security is good for preventing school shootings, such as the ones we enacted after Sandy Hook. We can at least make sure we know which non-students are coming in the front doors. However, when the potential shooters are your students, you have to work WITH your students, get to know them, teach other students the signs and etc.
We have over emphasized "bullying" by the way, and it relates to what beagle has been saying. We now extend "bullying" to mean isolating students who other students intrinsically understand as dangerous. That's not "bullying". That's human instinct. Think about your 14 yo daughter seeing Ethan Crumbley sitting by himself in the cafeteria. In the past it would be acceptable for her to simply leave him be. Now, we press her to override instincts that say "nope, hard pass" and approach him, maybe befriend him, because he is a loner.
We need to STOP telling children they must include loners and instead, as adults, follow through with loners persistently. WHY are they loners. Etc.
We need to restructure schools so that we get to know students better. The secondary schools in my district took a big step toward this in the last couple of years. So that kids like EC don't just wander from class to class unknown, but have at least one teacher who knows him consistently day to day, maybe year to year even.
These are just a couple of ideas, but ones that would work even in bigger high schools. Would they 100% prevent school shootings? Probably not. But they would help.